pwm to control a dc motor

Hello, i am trying to control a dc motor( 3V) with a CI 555 and one transistor 2N2222,so when i change the value of my pot the speed of my motor must change too.
the voltage which i have at the output of my 555 is Vcc-1

this is the circuit:
http://imageshack.us/photo/my-images/834/problemaph.jpg/

so i need to know the values of R and R1 to get the next:

transistor:
in saturation Vc=Vcc-3=Ve
in cut-off Vc=Vcc Ve=0V

somebody could help me?

thanks

 

the transistor has gain aprox β=222

and the motor can comsume until 0.3A

 

R is for this:

i need R because i want the next at my transistor:

http://imageshack.us/photo/my-images/560/sinttulozgc.jpg/

and at the output of the 555 i always have Vcc-1, so i need R at the emisor of the transistor because in saturation(when my motor consume energy) i need fix Vcc-3,and get that the motor won´t have more than 3V

do you understand more or less? i don´t know so much english and it is difficult to explain this

 

then,how could i fix 3V in my dc motor in saturation? because the 555 need al least 4.5V of supply voltage,

so for example if i want Vcc=8V,in saturation i want to have Vc=Vcc-Vmotor=8-3=5V,so i need 5V at my emisor to get fix this 3V on my motor,yes?
so i though about put a resistor to get it,or maybe put a zener diode of 4.7V


because i want to fix 3V on my motor,and changing the duty cicle with my pot i would like to change the speed of the motor.
i don´t want to fix a duty cycle for one supply voltage,i want a supply voltage and can change my duty cicle from 0 to 100

i think that i need a voltage on my emisor in saturation to get this,i don´t know if this is possible?

 

ah ok
so the motor sees the effective voltage, not the peak voltage?

then my mistake is that i am trying to fix the peak voltage and later change the effective with the duty cycle?

which formula relationed the effective voltage with the peak voltage for a pwm signal?

 

sorry could you explain it more clear,i am new on this and it is little diffiucult at the beginning

the motor works from 1.5V to 3V and i want 3V, the supply voltage should be higher than 4.5V(minimun voltage which need the 555)

thanks

 

and are there a way to do it for example with duty cicle from 0 to 100%, or will i need more voltage range for my motor?

which formula are you using to relationed the duty cicle with the voltage which see my motor and Vcc?

 

but i refered for example this:

vcc=???
i fix 3V to 100% duty cycle
and i fix 1.5V to 0% duty cycle
so i would like to change the speed in a bigger range of duty cycle or something like that


not as i have now vcc=12V, 3V duty cycle 25%,1.5V duty cycle 0%

do you know what i mean? is it possible?

 

yes i know,but if i would put a diode with fix value at the emisor,could i get it without Vcc=3V?

 

ok,thanks
the formula is for example for Vcc=6V:
3/6=sqrt(duty cycle) or 3/6=duty cycle??

and one thing more,now i will generate the pwm signal with a module ni9401(digital output) of compact rio,i don´t know if you know it,but it will generate a pwm signal 5V and it need current between[100microA to 2mA], i thought about the next circuit:

http://imageshack.us/photo/my-images/338/crio.jpg/

is it correct?
and the transistor has gain 40 and the motor load 0.3A so i will need al least 0.3/40=7.5mA at the base, but the digital output that i said you must be [100microA to 2mA]
how could i down this current more, maybe a voltage divisor?
do you understand what i mean?

thanks